1. Field of the Invention
The present invention relates to amplifier circuits and more particularly to analog amplifier and comparator circuits with body voltage control.
2. Description of the Related Art
Silicon On Insulator (SOI) technology offers performance enhancements over bulk silicon technology for Complimentary Metal Oxide Semiconductor (CMOS) digital circuits. When properly designed, circuits implemented in SOI should exhibit a 20% to 30% performance advantage over the same circuit functions implemented in bulk silicon. Alternately, the performance can be exchanged for a factor of two reduction in power dissipation at the same operating frequency. Much of this performance gain is achieved by letting the body voltage float. This arrangement allows the body voltage to bootstrap during switching transients resulting in more rapid xe2x80x9cturn onxe2x80x9d characteristic in the switching transistors. SOI technology has been projected to cost about 10% more than bulk technology.
SOI technology would appear to be a poor choice for analog circuits. Most analog circuits require very close matching between the threshold characteristics of two or more transistors. Allowing the body voltage to float seriously erodes transistor matching. Matching can be restored by connecting the two transistor bodies to a common potential. This xe2x80x9csolutionxe2x80x9d renders the performance advantage of SOI largely moot while retaining the larger processing costs.
Certain applications require both analog and digital circuits to be fabricated on the same chip and in the same technology. International Solid State Circuits Conference 1999 paper WP 25.6: xe2x80x9cA SOI Specific PLL for 1 GHz Microprocessorsxe2x80x9d (incorporated herein by reference) is illustrative of the problems and limitations incurred when analog functions are forced into implementation with digital circuits in SOI technology. Therefore, there is a need for analog circuits to benefit from SOI technology.
It is, therefore, an object of the present invention to provide a structure for an amplifier circuit which includes transistors configured as a source-coupled differential pair and whose bodies are controlled with a scaled and shifted version of the input voltage using positive feedback.
The invention further includes at least two more sets of two transistors comprising current mirrors, wherein an output current from the pair of source-coupled differential transistors is directed to the two current mirrors. The current mirrors generate currents proportional to the input voltage. The currents from the two current mirrors are driven into a fourth set of diode-connected transistors configured as loads. The voltage produced by the fourth set of transistors is applied differentially to the body node on the first set of transistors as a positive feedback voltage. In this way the positive feedback voltage is a translated and scaled version of the input signal voltage applied to the first set of devices.
Another embodiment of the of the invention is an amplifier circuit including at least two complimentary pairs of source-coupled differential pairs of transistors, the source-coupled differential pairs of transistors including a body and a gate, and at least two diode connected field effect transistors connected to each of said complimentary pairs. The diode connected field effect transistors load the body and the gate of the pair of transistors with positive feedback signals.